RH dip pipe castable is a low-cement bonded corundum-magnesia alumina spinel monolithic for RH vacuum refining immersion pipes. It resists thermal shock and spalling, solving cracking and detachment from thermal expansion mismatch among shell, bricks and castable.
| Al₂O₃ content | ≥ 88% |
|---|---|
| MgO content | 3% – 8% |
| Bulk density | ≥ 3.00 g/cm³ |
| CCS (1500℃×3h) | ≥ 120 MPa |
| MOR (1500℃×3h) | ≥ 12 MPa |
| PLC (1500℃×3h) | ± 0.5% |
| Thermal shock (1100℃ water) | ≥ 10 次 |
| Service temperature | ≥ 1600℃ |
RH vacuum refining inserts two immersion pipes into molten steel through a vacuum vessel to perform degassing, decarburization, oxygen blowing, powder injection desulfurization, inclusion removal and temperature and composition homogenization. From inside outward, a dip pipe consists of magnesia-chromite (or chromia-free) ring bricks, self-flowing material, the steel shell and the outer castable. Working directly in steel above 1600°C for 30–40 minutes per heat, the dip pipe is the most refractory-intensive part of RH refining.
The outer castable suffers chemical attack from steel and slag, erosion from steel flow, and thermal shock during handling, preheating and immersion. Thermal expansion of steel shell and refractories differs by nearly an order of magnitude, so interface cracks develop at high temperature. Uncontrolled cracks lead to spalling of the outer castable, sinking of ring bricks and premature offline of the dip pipe.
Tabular corundum provides erosion resistance and strength; fused magnesia-alumina spinel improves slag resistance and thermal shock resistance. Reactive alumina and spinel micropowders with microsilica and superplasticizer achieve low-cement, low-water bonding. Larger critical particle size plus small additions of zirconia fibers and thermal shock stabilizers further improve spalling resistance and hot strength.
Interlock profiles and metal anchors at the ring-brick/castable interface improve bottom integrity. The castable is vibration-cast, cured and dried, then preheated to about 1100°C before use. Regular gunning maintenance controls crack growth and extends dip pipe life.
Henan Songrui New Refractory Materials Co., Ltd. supplies custom formulations with matching self-flowing materials.
Large thermal expansion mismatch among steel shell, ring bricks and castable creates interface stress and cracks. The solutions are better anchoring design and higher thermal shock resistance and hot strength of the castable.
Mainly on the outer lining and ring-brick joints of immersion pipes, also suitable for lower vacuum vessel lining; formulations can be customized.
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